Deployment method for ocean bottom seismometers

ABSTRACT

A method and apparatus for deployment and retrieval of ocean bottom seismic receivers. In one embodiment, the apparatus comprises a carrier containing a plurality of receivers attached to a remotely operated vehicle (ROV). The carrier comprises a frame in which is mounted a structure for seating and releasing said receivers. The structure may comprise a movable carousel or a movable conveyor or fixed parallel rails or a barrel. In the case of the barrel, the receivers are axially stacked therein. The structure is disposed to deliver said receivers to a discharge port on said frame, where the receivers are removable from said carrier. The apparatus includes a discharge mechanism for removing said receivers from said carrier. In another embodiment, the method comprises the steps of loading a carrier with a plurality of receivers, attaching said carrier to an ROV, utilizing said ROV to transport the carrier from a surface vessel to a position adjacent the seabed and thereafter utilizing said ROV to remove receivers from said carrier and place the receivers on the seabed. In yet another embodiment, an ROV adjacent the seabed engages a deployment line extending from the vessel. The deployment line is used to guide receivers attached thereto down to the ROV for “on-time” delivery and placement on the seabed.

BACKGROUND OF THE INVENTION

The present invention relates to the field of seismic exploration. Moreparticularly, the invention relates to a method and apparatus forseismic exploration, and most particularly to deployment and retrievalof ocean bottom seismometer systems in deep marine environments.

Seismic exploration generally utilizes a seismic energy source togenerate an acoustic signal that propagates into the earth and ispartially reflected by subsurface seismic reflectors (i.e., interfacesbetween subsurface lithologic or fluid layers characterized by differentelastic properties). The reflected signals (known as “seismicreflections”) are detected and recorded by seismic receiver unitspositioned at or near the surface of the earth, thereby generating aseismic survey of the subsurface. The recorded signals, or seismicenergy data, can then be processed to yield information relating to thelithologic subsurface formations, identifying such features, as, forexample, lithologic subsurface formation boundaries.

Typically, the seismic receiver units are arranged in an array, whereinthe array of seismic receivers consists of a single string of receiversdistributed along a line in order to record data from the seismiccross-section below the line of receivers. For data over a larger areaand for three-dimensional representations of a formation, multiplestrings of receivers may be distributed side-by-side, such that a gridof receivers is formed.

While the fundamental process for detection and recording of seismicreflections is the same on land and in marine environments, marineenvironments present unique problems due to the body of water overlayingthe earth's surface. In marine environments, even simple deployment andretrieval of seismic receiver units is complicated since operations mustbe conducted off the deck of a seismic exploration vessel, whereexternal elements such as wave action, weather and limited space cangreatly effect the operation. These factors have become even moresignificant as exploration operations have pushed to deeper and deeperwater in recent years.

Exploration in deep water has resulted in an increased reliance onseismic receiver units that are placed on or near the seabed. Thesedevices are typically referred to as “OBC” (Ocean Bottom Cabling) or“OBS” (Ocean Bottom Seismometer) systems. There are three main groups ofocean bottom apparatus generally used to measure seismic signals at theseafloor. The first type of apparatus is an OBC system, similar to thetraditional towed streamer, which consists of a wire or fiber cable thatcontains geophones and/or hydrophones and which is laid on the seabed,where the detector units are interconnected with cable telemetry. ForOBC systems, a seismic vessel will deploy the cable off the bow or sternof the vessel and retrieve the cable at the opposite end of the vessel.In most cases, three ships are required to conduct the overall operationsince, in addition to a seismic energy source vessel, a speciallyequipped vessel is necessary for cable deployment and a separate vesselis needed for recording. The recording vessel is usually stationary andattached to the cable, while the deployment vessel is generally inconstant motion along the receiver line deploying and retrieving cable.Because the recording vessel is in constant physical contact with thecable, the effort required to maintain the vessel's position to counterwave action and ocean currents can generate great tension within thecable, increasing the likelihood of a broken cable or failed equipment,as well as the introduction of signal interference into the cable.

A second type of recording system is an OBS system in which a sensorpackage and electronics package is anchored to the sea floor. The devicetypically digitizes the signals and uses a wire cable to transmit datato a radio unit attached to the anchored cable and floating on the watersurface. The floating transmitter unit then transmits the data to asurface vessel where the seismic data are recorded. Hundreds if notthousands of OBS units are typically deployed in a seismic survey. Athird type of seismic recording device is an OBS system known asSeafloor Seismic Recorders (SSR's). These devices contain the sensorsand electronics in sealed packages, and record seismic data on-boardwhile deployed on the seafloor (as opposed to digitizing andtransmitting the data to an external recorder). Data are retrieved byretrieving the device from the seafloor. SSRs are typically re-usable.

Each OBS system generally includes components such as one or moregeophone and/or hydrophone sensors, a power source, a crystal oscillatorclock, a control circuit, and, in instances when gimbaled geophones areused and shear data are recorded, a compass or gimbal. Many of thesecomponents are subject to various effects arising from the orientationof the OBS unit as it is deployed on the ocean bottom. For example,crystals are subject to gravitational effects, such that orientation ofthe OBS system can effect operation of a crystal clock. Anymisorientation of the OBS system on the seabed can result in clockinaccuracies. Likewise, while mechanical gimbals may be used to correctfor tilt, pitch in many mechanical gimbal devices is limited 30°. Forsuch devices, in order for the gimbal to function properly, the OBSsystem must be deployed on the seabed in substantially the desiredorientation, i.e., approximately 30° from the horizontal or less. Ofcourse, it is well known that mechanical gimballing of a geophone isexpensive and requires more space than a non-gimballed geophone, and assuch, it is desirable to deploy an OBS system so as to render gimballingunnecessary.

As with orientation, the location of OBS system on the seabed isnecessary to properly interpret seismic data recorded by the system. Theaccuracy of the processed data depends in part on the accuracy of thelocation information used to process the data. Since conventionallocation devices such as GPS will not operate in the water environments,traditional prior art methods for establishing the location of the OBSsystems on the seabed include sonar. For example, with a sonar system,the OBS device may be “pinged” to determine its location. In any event,the accuracy of the processed data is directly dependent on theprecision with which the location of the OBS system is determined. Thus,it is highly desirable to utilize deployment methods and devices thatwill produce dependable location information. In this same vein, it ishighly desirable to ensure that the planned positioning of the OBSdevice on the seabed is achieved.

One problem that is common in all types of seismic systems physicallydeployed on the seabed is the degree of coupling between the system andthe seabed. Those skilled in the art will understand that the physicalcoupling between a seismic unit and the earth has become one of theprimary concerns in the seismic data collection industry. Effectivecoupling between the geophones of a system and the seabed is paramountto ensuring proper operation of the system. For example, in an OBCsystem where three-dimensional geophones are employed, because the cableis simply laid on the seabed, geophones are not rigidly coupled to thesediment on the seabed. As such, horizontal motion other than that dueto the sediment, such as for example, ocean bottom currents, can causeerroneous signals. Likewise, because of its elongated structure, OBCsystems tend to have satisfactory coupling only along the major axis ofthe cable when attempting to record shear wave data.

To enhance coupling, many OBS systems of the prior art separate sensingunits, i.e., the geophone package, from the remainder of the electronicsto ensure that the geophones are effectively coupled to the seabed.

Thus, orientation, positioning and coupling of an OBS unit are allimportant factors in achieving effective operation of a seismic unit andcollection of seismic data. Each of these placement components is highlydependent on the manner in which the OBS units are deployed. Typically,for operations in coastal transition zones such as shallow water ormarshes, units are simply dropped in a water column over the side of adeployment vessel above the targeted seabed position. Because the watercolumn is comparatively shallow and the OBS unit is relatively heavy,the effects of ocean currents, drag and the like is minimal and thedesired positioning of the OBS unit on the seafloor can be fairly easilyachieved. In contrast, an OBS unit dropped through hundreds or thousandsof feet of water and subject to the forces of buoyancy, drag and oceancurrents could settle on the seabed as much as several hundred feet fromits original position. Not only is the unit likely to be of little valuein the seismic survey because of its misplacement, locating andretrieving the OBS unit becomes much more difficult.

Of course, orientation is often less certain than positioning. Variousobjects, whether rocks, reefs or even discarded debris, can disrupt thedesired orientation of a unit, which in most cases is preferablyparallel with the horizontal. Those skilled in the art will understandthat orientation can effect data accuracy. The most accurate data isdata that has been processed to account for the orientation of theseismic collection unit that acquires the raw data. Such processingtypically necessitates additional equipment on-board the unit itself todetermine x, y and z orientation, as well as additional computationalpower and time during processing of the raw data.

Likewise, the degree of coupling between a seismic collection unit andthe sea floor, whether in shallow water or deep water, is oftendifficult to determine at the time a unit is positioned. This isparticularly true of seismic units that are simply allowed to settlewhere they land. In many cases, the top layer of silt at a particularlocation on the sea floor may be somewhat unstable or mushy, such thatseismic energy transmission therethrough to the seismic unit isattenuated or distorted in some way. Even in the case of relatively hardor compact sea floors, if a seismic unit has not formed a good couplingwith the earth, seismic energy passing from the earth to the unit'sgeophones may be attenuated. Thus, even if a unit is positioned in thedesired location and oriented to minimize gravitational effects and thelike on seismic data, a high degree of coupling must still be achievedin order to maximize the quality of the collected data.

Thus, based on the foregoing, it is highly desirable to be able to placeOBS units on the sea floor of deep water locations so as to ensure thedesired positioning and orientation is achieved and to maximize couplingbetween the unit and the sea floor.

Because the push to conduct seismic operations in deep water isrelatively recent, few attempts have been made to address theabove-mentioned problems associated with deep water deployment of OBSunits. U.S. Patent Application Publication US 2003/0218937 A1 disclosesa method for OBS deployment utilizing a tethered remote operatingvehicle (“ROV”) and a separate OBS carrier cage, each lowered to theseabed on a separate line. The carrier contains a plurality of OBSunits. The reference teaches that once the ROV and carrier cage arepositioned adjacent the seabed, the ROV can be used to extract and placeeach OBS unit in the desired location around the carrier. In a preferredembodiment, a plurality of carriers are used to simultaneously lower alarge group of OBS units close to the seabed at one time so as tomaximize the operational time of the ROV.

Those skilled in the art will understand that such a system will likelyencounter operational problems in light of the rigors of deep wateroperations where extreme depths, surface conditions, multiple oceancurrents and mushy or unstable sea bottom conditions can allsignificantly affect the deployment effort Most notably, the drag on thecarrier, the ROV and their respective lines are all different, and assuch, these different components of the deployment system will havedisparate responses under water when subject to the various elements. Inthe case of the carrier cage, there is no mechanism for remotelycontrolling the position of the cage in the water, the result being thatthe cage is highly likely to be pulled along in the direction of theprevailing ocean currents with very little control over the cage'smovement. In this same vein, the tether for the ROV and the line for thecarrier cage are likely to be of different dimensions and buoyanciessuch that drag on the lines is likely to differ substantially. Whendeployed in thousands of feet of water, the effects of drag on thesevarious elements of the prior art system are significantly magnified,such that the ROV and the carrier cage could be hundreds of feet or moreapart.

Perhaps even more threatening to such a system under actual operatingconditions is the likelihood that the lines will become tangled,interrupting a seismic shoot and threatening profitability. Thoseskilled in the art understand that as the number of lines in the waterat any given time increases, the more complicated the operation becomesand the more difficult it becomes to control movement of the lines andprevent tangling. This is particularly true where the lines, as well asthe objects attached at the lower ends of the lines, have different dragcharacteristics. Even when the end of one line is controlled by an ROV,but the other is not, entanglement is likely. As an example, each linemay be as long as 10,000 feet extending from the surface of the water tothe seabed. Since a typical deployment boat may be only 40 feet wide andeach line is deployed on opposite sides of the boat, there is a highprobability that the carrier cage line will become entangled with theROV tether.

An additional drawback to the above-described prior art system is thatit utilizes only a single ROV for deployment and retrieval. While such asystem minimizes the cost of operations, the entire operation isdependent on the operability of the single ROV. Any breakdown of the ROVcan substantially delay the deployment/retrieval efforts since repairswould be necessary before continuing.

Thus, it would be desirable to provide a deployment system for deepwater seismic data collection units that minimizes the effects of drag,weather, ocean currents, depth and similar conditions on OBS deploymentoperations at or near the seabed. Additionally, such a system preferablywould be disposed to retrieve previously deployed OBS units. Such asystem should permit accurate placement and orientation on the seabedand good coupling of individual OBS units therewith. Preferably, such asystem would utilize an ROV to deploy and/or retrieve multiple OBS unitsat or near the seabed in a manner that maximizes use of the ROV in theoperations. The system should provide minimum likelihood of entanglementof lines if more than one line is used in the same operation. The systemshould also provide for efficient turn-around of OBS units that havebeen retrieved from deployment. Such turn-around would desirably includedata extraction and recharging of the OBS units. In the preferredembodiment, the deployment system would also minimize the effects ofequipment breakdown on the overall seismic acquisition operation.

OBS units deployment should be easily accomplished, yet the OBS unitsshould be deployable at a certain location with a high degree ofconfidence.

The system should also be capable of readily handling the hundreds orthousands of OBS units that comprise an array for deployment in oceanenvironments. Such a system should be able to deploy, retrieve, track,maintain and store individual recorder units while minimizing manpowerand the need for additional surface vessels. The system should likewiseminimize potential damage to the individual units during such activity.

SUMMARY OF THE INVENTION

The present invention provides a system for deep water deployment andretrieval of OBS units from a surface vessel or platform. The systemutilizes at least one remotely operated vehicle (“ROV”) or similardevice to which is attached a carrier apparatus in which is seatedmultiple, independently deployable OBS units. In most of the preferredembodiments, the carrier apparatus is attached directly to the ROV. Assuch, the ROV itself is used to carry the OBS units down to the seabedfrom the surface vessel. Once adjacent the seabed, the ROV canefficiently move between desired “node” locations in order to plant anOBS for operation. Preferably, the individual units can either beautomatically ejected from the carrier apparatus or alternativelyextracted and placed with the assistance of a robotic arm or similarmanipulation device carried on the ROV/carrier system.

In one preferred embodiment, the carrier apparatus consists of a movingor rotating carousel on which the OBS units are carried. The carouselrotates in order to position an OBS unit for deployment from thecarrier. Such deployment may be automatic or require externalassistance, such as a robotic arm located on the carrier or ROV. Acarousel such as this is desirable because it not only simplifiesdeployment from the carrier, but it also permits the carrier “load”,i.e., the OBS units, to be shifted in order to control weight balanceand buoyancy of the ROV/carrier system.

In another preferred embodiment, the carrier apparatus is a barrel intowhich is loaded multiple OBS units. The barrel is attached to the ROV sothat the OBS units can be discharged from an end of the barrel, againeither automatically or with external assistance. The barrel may also beutilized to retrieve OBS units from deployment on the seabed.

In yet another preferred embodiment, the carrier is provided with one ormore movable conveyor belts. OBS units are disposed on the conveyorbelts which are operable to move the OBS units to a discharge positionon the carrier. As with the carousel mentioned above, the conveyorbelt(s) can be utilized to shift OBS units within the carrier so as tocontrol weight balance and buoyancy. The conveyor belt(s) may also beutilized to retrieve the OBS units from deployment on the seabed.

In still another preferred embodiment, the OBS units are carried onrails that form a part of the carrier apparatus. The OBS units aredisposed to slidingly move along the rails in order to move them to adeployment position on the carrier. The rails may also be utilized toengage the OBS units for retrieval from the seabed.

In another preferred embodiment, OBS units are sequentially delivered tothe seabed utilizing an “on time” delivery system so that an OBS unitarrives for deployment just as the ROV is moving into position forplacement of the unit. In this preferred embodiment, each OBS unit istransported down a delivery line that runs substantially parallel withthe ROV's tether. The delivery line is attached to the ROV so as to movein conjunction with the ROV. Alternatively, the delivery line may form apart of the ROV tether itself. In either case, the delivery line isdisposed to deliver OBS units adjacent an ROV robotic arm or similardevice so as to permit the OBS unit to be removed from the delivery lineand positioned by the ROV for operation. Because of the relatively longtravel time necessary for an OBS unit to travel down a delivery linefrom a deployment vessel to an ROV, multiple OBS units may be travelingdown the delivery line simultaneously, albeit spaced apart accordingly,to permit the ROV to deploy an OBS unit prior to the arrival of the nextOBS unit.

In another embodiment of the “on time” delivery system, the OBS unitsare sequentially delivered to the seabed by utilizing a deployment andretrieval line having the units attached thereto at intervals compatiblewith the desired placement spacing. At the ocean surface, a marinevessel pays out the deployment line with the attached units, while at ornear the seabed a guide disposed on an ROV engages the line and movesalong a desired layout line. Movement of the ROV along the layout linecauses the deployment line to be drawn through the water column and passthrough the guide. As an OBS unit passes through the guide, the unit isplaced or “planted” on the seabed by the ROV. After a unit is placed,the ROV continues to move along the desired line layout, thereby causingthe next OBS unit attached to the deployment line to be drawn throughthe guides. Preferably, the ROV arrives at the next desired OBS unitdeployment location just as the next OBS unit on the deployment line isarriving at the seabed. This process continues until all OBS units for adesired line layout have been deployed.

In the preceding embodiment of the invention, an anchor weight may beattached to the deployment line a distance from the final OBS unit thathas been placed for the layout. The anchor unit is placed on the seabedby the ROV so as to maintain a desired slack between the final unit andthe anchor. Preferably, a buoy is attached to the anchor with a buoyline while an acoustical release device attached to the buoy line causesthe buoy to “float” a distance below the surface of the water. Uponactivation of the release device, the buoy will float to the surface soas to permit the deployment line with attached OBS units to beretrieved.

In each case, by utilizing an ROV or similar remote deploymentmechanism, OBS units can be placed accurately on the seabed in thedesired position. Likewise, proper orientation can be ensured, as can ahigh degree of coupling. In the preferred embodiment, each OBS unit iswireless and self-contained so that no communication or control isrequired between the ROV and the OBS units. In this embodiment,operation of the OBS units is initiated prior to deployment from thedeck of the deployment vessel, or alternatively, prior to handling bythe ROV at the seabed. In another embodiment, the OBS unit and the ROVare each equipped with a wireless communication device, such as anacoustic or electromagnetic modem, so that the ROV can be utilized tocommunicate with the OBS unit when the unit and the ROV are in“wireless” range of one another. This permits communication with the OBSunit for purposes such as activation, operation and quality control.

The ROV/carrier system can also be utilized to retrieve deployed OBSunits from the seabed and transport them back to the surface vessel. Acarrier containing retrieved OBS units can be detached from the ROV atthe surface and moved to a location on the vessel for processing andservicing of the OBS units. Preferably, such units are removed from thecarrier and seismic data extraction takes place on the deck. Thereafter,the OBS units are charged, tested, re-synchronized, and OBS unitoperation is re-initiated. OBS units that have been processed in thisregard can be loaded back into the carrier for reuse.

Preferably, each OBS unit is self contained such that all of theelectronics are disposed within the OBS unit's case, including amulti-directional geophone package, a seismic data recording device, apower source and a clock. A wireless communication device also may beincluded for communication between the ROV and OBS. The power source ispreferably rechargeable batteries.

Preferably, each OBS unit is activated while on-board the seismic vesseland deactivated once retrieved from the ocean, such that the unit iscontinuously acquiring data during a time period beginning before theROV begins a trip down to the seabed. Alternatively, to the extent awireless communication device is present on the ROV and in the OBSunits, recording is initiated through the ROV communication link at ornear the time the OBS unit is deployed by the ROV.

A robotic arm, overhead gantry, crane or the like may be positioned onthe deck to move carriers and ROVs. Likewise, the vessel would includean OBS unit handling system to load and unload carriers, as well as toperform various tasks on the OBS units, such as data extraction, testingand charging.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of seismic operations in deep waters showingdeployment of autonomous OBS receiver units using the ROV/carrier systemthat is the subject of the present invention.

FIG. 2 is perspective view of carrier system employing a movingcarrousel to manipulate OBS units.

FIG. 3 is a cut-away top view of a carrousel type carrier system of FIG.2.

FIG. 4 is a perspective view of the carrier system employing a barrel tocontain OBS units.

FIG. 5 illustrates one embodiment of the barrel type carrier attached toan ROV.

FIG. 6 is a top view of a carrier system employing conveyor belts tomanipulate OBS units.

FIG. 7 is a side view of a conveyor belt utilized in the carrier of FIG.6

FIG. 8 is a cut-away side view of a carrier system employing rails todeliver OBS units.

FIG. 9 is a cut-away top view of the carrier of FIG. 8.

FIG. 10 is an end view of an OBS unit deployed on the rails of thecarrier of FIG. 8.

FIG. 11 is a schematic view of seismic operations in deep waters showingdeployment of OBS receiver units using an ROV and one embodiment of the“on time” delivery system that is the subject of the present invention.

FIG. 12 is a schematic view of seismic operations in deep water showinganother embodiment of “on time” deployment of OBS receiver units byutilizing an ROV to place units attached to a deployment line payed outfrom the surface.

FIG. 13 is a cut away top view of the deployment line guide disposed onthe underside of an ROV.

FIG. 14 is a schematic view of a plurality of autonomous, interconnectedOBS units laid out on the seabed with a retrieval buoy and acousticrelease device attached thereto.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the detailed description of the invention, like numerals are employedto designate like parts throughout. Various items of equipment, such asfasteners, fittings, etc., may be omitted to simplify the description.However, those skilled in the art will realize that such conventionalequipment can be employed as desired.

With reference to FIG. 1, there is shown a body of water 10 having asurface 12 and a seabed 14. A vessel or operations platform 16 ispositioned on the surface 12 of the water 10. A remotely operatedvehicle (“ROV”) or similar device 18 is in communication with vessel 16.A carrier 20 is attached to ROV 18. Carrier 20 is disposed for receiptof a plurality of ocean bottom seismic receiver units 22. ROV 18 iscapable of moving between surface 12 and seabed 14 in order to ferryocean bottom seismic receiver units 22 therebetween. ROV 18 may also beutilized to remove units 22 from carrier 20 and place units 22 on seabed14. Likewise, ROV 18 may be utilized to retrieve units 22 from seabed 14and insert units 22 into an empty or partially empty carrier 20.Alternatively, carrier 20 may be disposed to eject or otherwise cause tobe removed units 22 therefrom for deployment on seabed 14.

ROV 18 and seismic operations related to units 22 are preferablyconducted off of the same vessel or platform, in the illustrated case,vessel 16. While any type of underwater vehicle can be utilized for suchoperations, including without limitation, a submarine or an autonomousunderwater vehicle (AUV), ROVs as are commonly utilized for all types ofunderwater operations are contemplated in the preferred embodiment. SuchROVs are typically in communication with the surface vessel or platform16 via an umbilical cord or tether 24, which is used to provide power,communications and control. Commonly, a tether management system or“TMS” 26 may be utilized as an intermediary, sub surface platform fromwhich to operate an ROV. A TMS is typically also a controllable platformdisposed to carry and pay out a long length of tether 24, such as forexample 1600 meters. For most ROV 18 operations at seabed 14, TMS 26 canbe positioned approximately 50 feet above seabed 14 and can pay outtether 24 as necessary for ROV 18 to move freely about at seabed 14 inorder to “plant” OBS units 22 thereon.

Turning to FIGS. 2 and 3, there is shown an ROV 18 attached to a carriersystem 20 employing a moving carrousel 30 on which are seated aplurality of OBS units 22. Carrier system 20 is defined by a frame 32 inwhich carrousel 30 is mounted and on which a discharge port 34 isdefined. Carousel 30 is comprised of circular pod guide 36 on which aremounted a plurality of seats 38 in which units 22 can be seated. In oneembodiment, pod guide 36 is a rigid wheel. In an alternative embodiment,pod guide 36 is a movable track. In any event, wheel/track 36 is definedby an inner perimeter 40 and an outer perimeter 41. Disposed along saidinner perimeter 40 are gear teeth 42. A drive motor 44 having a drivegear 46 is positioned adjacent inner perimeter 38 so that drive gear 46of motor 44 can engage gear teeth 42 of wheel/track 36. Carrier system20 is attached to ROV 18 via center shaft 48.

In one preferred embodiment, carrier system 20 is pivotally attached tocenter shaft 48 while drive motor 44 is rigidly fixed to ROV 18 so thatactivation of drive motor 44 causes the entire carrier system 20 torotate on shaft 48 relative to ROV 18. In this configuration, anadditional drive motor may be provided to rotate frame 32 relative tocarousel 30. In such case, frame 32 and carousel 30 may be separatelypivotally mounted on center shaft 48. Rotation of carousel 30 relativeto frame 32 permits individual seats 38 to be selectively positionedadjacent discharge port 34.

In another embodiment frame 32 is rigidly attached to ROV 18 and onlycarousel 30 is pivotally attached to center shaft 48. Drive motor 44 isrigidly attached to either ROV 18 or frame 32 so that activation ofdrive motor 44 causes carousel 30 to rotate within frame 32 so as tomove individual seats 38 adjacent discharge port 34.

Frame 32 is also provided with guides 50 that maintain the alignment ofcarousel 30 within frame 32.

A variety of discharge mechanisms may be used to cause an OBS unit 22 tobe deployed from carrier 20 via discharge port 34. In one embodiment,frame 32 includes a spring mechanism 52 a adjacent port 34 whereinspring mechanism 52 urges unit 22 through port 34. In anotherembodiment, frame 32 may include a pivotal release lever or door 52 bthat blocks discharge port 34. Door 52 b can be selectively activated toopen, thereby permitting a unit 22 seated adjacent discharge port 34 tobe deployed therethrough.

Commonly ROVs such as ROV 18 are provided with at least one robotic arm,such as is indicated at 54. Robotic arm 54 may be used in thealternative to the above described discharge mechanisms or in concerttherewith. Furthermore, carrier 20 may be provided with its own roboticarm. In any event, robotic arm 54 includes a clamping mechanism 56 thatcan engage a unit 22 and extract said unit from discharge port 34.

Those skilled in the art will understand that upon discharge of a unit22 from carrier 20, the weight, balance and buoyancy of the ROV/carriersystem is changed. By utilizing a movable carousel 30 as describedabove, the carrier load, i.e., the remaining OBS units 22, can berotated to re-adjust weight distribution and ensure desired balance ofthe system. In this regard, it is desirable to launch OBS units 22 in analternating fashion relative to their position on carousel 30 so as tomaintain a substantially uniform balance for the overall system. Forexample, carousel 30 is rotated so as to cause units approximately175°-185° apart on wheel 36 to be sequentially launched.

FIGS. 4 and 5 illustrate another preferred embodiment of the inventionin which carrier 20 is comprised of a barrel 60 into which is loadedmultiple OBS units 22. Barrel 60 has a first end 62, a second end 64with a chamber 66 therebetween and is defined along a central axis 68.Barrel 60 is mounted on a frame 69 and disposed to receive multiple OBSunits 22 axially stacked within chamber 66 along central axis 68. Atfirst end 62, barrel 60 is provided with a discharge port 70 throughwhich units 22 can be discharged from chamber 66. Discharge port 70 mayinclude a locking ring 72 disposed around a flared portion 74 of theinner perimeter of first end 62 of barrel 60. Buoyancy material 73 maybe attached to carrier 20.

A pump 76 is in fluid communication with inner chamber 66, preferablythrough a port 78 provided adjacent the second end 64 of chamber 66, andis utilized to pump sea water into chamber 66 as units 22 are dischargedtherefrom. Those skilled in the art will appreciate that when units 22are disposed within barrel 60, each unit snuggly fits within theperimeter of barrel 60 thereby permitting pump 76 to build up a head ofpressure within chamber 66 so as to urge units 22 axially towardsdischarge port 70. Additionally, water pumped into chamber 66 by pump 76can be utilized to control the buoyancy of carrier 20. In this regard,disks 78 formed of a buoyant material may be sandwiched between adjacentOBS units 22 to add further buoyancy to carrier 20.

In the preferred embodiment, a robotic arm 80 of ROV 18 is utilized todischarge units 22 from barrel 60. In this embodiment, robotic arm 80includes a clamping mechanism 82 that engages the unit 22 seated indischarge port 70. Clamping mechanism 82 may be comprised, in oneillustrative and non-limiting instance, of a suction cup 83 that canengage unit 22. Clamping mechanism 82 may further include a lockingflange 84 that seats within locking ring 72 during extraction of an OBSunit 22. Once the clamping mechanism is secured in locking ring 72, thepressure head from barrel 60 can be utilized to urge an OBS unit 22 intoengagement with clamping mechanism 82, at which point clamping mechanism82 is detached from discharge port 70 so as to withdraw unit 22therefrom. Alternatively, clamping mechanism 82 may further comprise abiased plunger mechanism 85 attached to locking flange 84 and disposedto axially move suction cup 83 into engagement with unit 22 once lockingflange 84 is seated in locking ring 72.

In another embodiment, units 22 can be automatically discharged fromdischarge port 70 under the pressure head from barrel 60. In thisembodiment, a unit 22 seats in flange 72. Once a predetermined pressureis achieved within barrel 60, flange 72 releases the unit and the nextsequential unit seats in flange 72. Such a configuration permits thecarrier 20, and specifically discharge port 70, to be positionedadjacent seabed 14 at the desired location for “planting” an OBS unit 22thereon. As such, units 22 that are released from flange 72 drop intoplace on seabed 14 without the need for further manipulation.

An alternative embodiment utilizes an additional discharge mechanism,such as a spring or similar biasing element, positioned within barrel 60to urge units 22 axially along barrel 60 and out through discharge port70.

While the barrel-type carrier 20 has been described with a singlebarrel, those skilled in the art will appreciate that such aconfiguration will work equally well with multiple barrels aligned inparallel such as is specifically illustrated in FIG. 5.

The barrel 60 may also be utilized to retrieve OBS units from deploymenton the seabed 14. Specifically, such retrieval can be accomplished bypositioning discharge port 70 of barrel 60 over a deployed OBS unit sothat said unit is axially aligned with barrel 60 and thereafter loweringthe flared portion 74 of barrel 60 around said unit 22 until thedeployed unit 22 seats within discharge port 70. As subsequent deployedunits 22 are retrieved, retrieved units 22 will be caused to moveaxially along barrel 60 towards second end 64.

FIGS. 6 and 7 illustrate another embodiment of carrier 20 in whichcarrier 20 comprises a frame 90 and one or more movable conveyor belts92 mounted on frame 90. In FIG. 6, three conveyor belts 92 areillustrated. Each conveyor belt 92 is defined by a first end 94 and asecond end 96 and comprises a flexible belt or track 98 and at least tworollers 100 on which belt 98 is mounted. Frame 90 is provided with atlest one discharge port 102. Conveyor belt 92 is disposed for receipt ofa plurality of units 22 and is positioned in frame 90 so that second end96 of conveyor belt 92 is adjacent discharge port 102. Actuation ofconveyor belt 92 causes units 22 seated thereon to be moved from a firstposition to a second position. Such actuation can be used to both“adjust” the weight distribution of units 22 seated in carrier 20, aswell as deliver units 22 to a position adjacent discharge port 102.Buoyancy material 103 may also be attached to carrier 20 in order tofurther assist with weight and buoyancy control.

In one embodiment, deployment of a unit 22 simply involves positioningcarrier 20 adjacent the seabed 14 at the desired location where a unit22 is to be planted. Once in position, a unit 22 can simply be rolledoff of the second end 96 of conveyor belt 92. Frame 90 may include aguide 104 to ensure that a deployed unit 22 remains properly oriented asit is deposited on seabed 14.

In another embodiment, a variety of discharge mechanisms may be used tocause an OBS unit 22 to be deployed from carrier 20 via discharge port102. In one embodiment, frame 90 includes a spring mechanism 52 aadjacent port 102 wherein spring mechanism 52 urges unit 22 through port102. In another embodiment, frame 90 may include a pivotal release leveror door 52 b that blocks discharge port 102. Door 52 b can beselectively activated to open, thereby permitting a unit 22 seatedadjacent discharge port 102 to be deployed therethrough.

A robotic arm 54 may be used in the alternative to the above describeddischarge mechanisms or in concert therewith. Robotic arm 54 preferablyincludes a clamping mechanism 56 that can engage a unit 22 and extractsaid unit from discharge port 102.

In the illustrated embodiment, conveyor belt 92 is linear, althoughconveyor belt 92 may be non-linear for purposes of the invention.Likewise, while conveyor belt 92 is illustrated as a flexible belt,conveyor may be a track or similar mechanism to provide conveyance of aunit 22 from a first position to a second position.

This conveyor-type carrier 20 may also be used to easily retrieve unitsand convey them back to vessel 16. Units 22 deployed on the seabed 14may be engaged directly by conveyor belt 92 or may be engaged by roboticarm 54 and placed on conveyor belt 92 adjacent port 102. Conveyor belt92 may then be activated to move the unit 22 toward first end 94,thereby making space available on conveyor belt 92 adjacent port 102 foranother retrieved unit. Such a mechanism is also desirable for loadingunits 22 into carrier 20 for transport and deployment since units 22 canbe quickly “fed” into carrier 20 as conveyor belt 92 is moving.

With reference to FIGS. 8, 9 and 10, there is shown another embodimentof carrier 20 in which OBS units 22 are carried and slidably movable onparallel rails 110 mounted within a frame 112. In the illustratedembodiment, rails 110 are rigidly mounted within frame 112 and form alinear path for movement of units 22 thereon. In another embodiment,parallel rails 110 form a non-linear path. Further, while only one setof rails 110 may be used, preferably three parallel sets of rails areutilized to increase the number of units 22 that can be carried bycarrier 20. In any event, rails 110 are defined by a first end 114 and asecond end 116, wherein the second end 116 of said rails terminateadjacent a discharge port 118 provided in frame 112.

Also positioned adjacent discharge port 118 are movable deployment rails120. Deployment rails 120 are disposed to move perpendicular to rails110 from a first position in which deployment rails 120 are aligned withrails 110 to a second position in which deployment rails 120 aredisposed to release and/or engage units 22. In the preferred embodiment,a piston 122 is used to move deployment rails 120 between the first andsecond positions. A fence 121 or similar barrier may be attached todeployment rails 120 perpendicular thereto so as to be positionedadjacent discharge port 118 when deployment rails 120 move to the secondposition, thereby preventing a unit 22 disposed on rails 110 adjacentthe discharge port 118 from sliding off of rails 110. Deployment rails120 may also be disposed to partially rotate and/or move out from frame112 as rails 120 travel to the second position, thereby facilitatingrelease of an OBS unit therefrom.

Deployment rails 120 are further defined by a first end 124 and a secondend 126. When deployment rails 120 are in the first position, first end124 thereof is aligned with the second end 116 of rails 110 so thatunits 22 can slide therebetween. The second end 126 of rails 124 may betapered to form a fork, as shown at 127, to facilitate engagement of OBSunits 22. Specifically, the forked second end 126 of rails 124 can beutilized to engage and retrieve OBS units 22 that are deployed on seabed14.

Units 22 are disposed to slidingly move along rails 110 and 124. In onepreferred embodiment illustrated best in FIGS. 8 and 10, units 22 mayinclude a cap 128 having opposing sides 130 that are notched as is shownat 132 for engagement by said rails 110 and 124. Cap 128 may form a partof unit 22 or may be removably attached thereto. Furthermore, cap 128may be formed of a buoyant material such as foam in order to lighten theoverall load of carrier 20. Likewise, frame 112 may have a buoyantmaterial 134 attached thereto.

A variety of discharge mechanisms may be used to cause an OBS unit 22 tobe deployed from deployment rails 124. In one embodiment, frame 112includes a spring mechanism 52 a adjacent port 114 wherein springmechanism 52 urges unit 22 through port 114 onto rails 124. In anotherembodiment, frame 112 may include a pivotal release lever or door 52 bthat blocks discharge port 114. Door 52 b can be selectively activatedto open, thereby permitting a unit 22 seated adjacent discharge port 114to be deployed therethrough onto deployment rails 124. Similar dischargemechanisms may be utilized on rails 124 to deploy a unit 22 seatedthereon.

A robotic arm 54 may be used in the alternative to the above describeddischarge mechanisms or in concert therewith. Robotic arm 54 preferablyincludes a clamping mechanism 56 that can engage a unit 22 and extractsaid unit from rails 124.

As shown in FIG. 8, a rail-type carrier 20 as described above ispreferably attached to the bottom of ROV 18 so that the overall centerof gravity of the ROV/carrier system remains low and ROV 18 remains inan upright position.

In each case of the above-described carriers, the carrier is attached tothe lower portions of ROV 18 so that the center of gravity of theoverall ROV/carrier system is lower than the center of buoyancy for thesystem. In the event of a loss of power, the system will remain uprightand can more easily be retrieved.

Additionally, in each of the above-described embodiments, multiple OBSunits are shuttled down to the seabed and back to the surface utilizingan ROV and more specifically, a carrier attached directly to the ROV.This eliminates the need for separate baskets as described in the priorart and the drawbacks associated therewith.

In another preferred embodiment of the deployment method, as illustratedin FIG. 11, OBS units 22 are sequentially delivered to the seabed 140from a vessel or platform 142 by sliding units 22 down a deployment line144 to an ROV 18 positioned adjacent seabed 140. Deployment line 144 isdefined by a first end 146 attached to vessel 142 and a second end 148attached to ROV 18. ROV 18 may be operated from a tether managementsystem 26 or directly from vessel 142 by way of a tether or umbilicalcord 24. Preferably, deployment line 144 runs substantially parallel totether 24, or alternatively, deployment line 144 forms a part of tether24 or is otherwise secured to tether 24. Deployment line 144 is attachedto ROV 18 so as to permit OBS units 22 sliding down line 144 to beremoved therefrom and placed on the seabed in the desired location.Deployment line 144 is attached to the ROV 18 so as to move inconjunction with ROV 18, obviating the need for ROV to return to acentral location to retrieve OBS units 22 for deployment.

A robotic arm 154 is preferably used to remove OBS units 22 fromdeployment line 144 and place units 22 on seabed 140. ROV 18alternatively may be provided with a launch device to which line 144 isattached, whereby the launch device causes OBS units 22 to be disengagedfrom line 144 and released onto the seabed 140.

In an alternative embodiment of this method, second end 148 ofdeployment line 144 is attached to a fixed object 150 or secureddirectly to the seabed 140. In each case, however, the delivery methodpermits OBS units 22 to be transported down deployment line 144 forreceipt and deployment by ROV 18.

The method as described herein provides an “on time” OBS unit deliverysystem so that a unit 22 arrives for deployment just as ROV 18 is movinginto position on seabed 140 for placement of unit 22. Such a systemeliminates the need for the prior art basket system in which an ROV wasconstantly required to return to a central distribution point and theneed for independent, free-floating lines in the water. Those skilled inthe art will appreciate that to the extent the deployment line 144 isattached to ROV 18, deployment line 144 is drivable, hence thelikelihood of entanglement with other lines is significantly reduced.

Furthermore, because of the relatively long travel time necessary for anOBS unit 22 to travel down deployment line 144 from vessel 142 to ROV18, multiple OBS units 22 may be traveling down deployment line 144simultaneously, albeit spaced apart accordingly, to permit ROV 18 todetach and “plant” an OBS unit 22 prior to the arrival of the next OBSunit.

In another preferred embodiment of the “on time” deployment method, asillustrated in FIG. 12, OBS units 22 are attached at spaced intervalsalong a deployment line 144 that is payed out from a surface vessel orplatform 142 and placed on the seabed 140 by an ROV 18 as the ROV 18moves along a desired layout path on seabed 140. Deployment line 144,which may be a continuous cable or a set of interconnected segments, isof sufficient length to accommodate the placement of a desired number ofOBS units 22 along a layout line. The OBS units 22 are attached to thedeployment line 144 at intervals sufficient to allow proper deploymentspacing along the layout line, taking into account the added lengthneeded for possible seabed 140 irregularities.

More specifically, as further illustrated in FIG. 13, line 144 isengaged by a guide 143 disposed on ROV 18. In one preferred embodiment,guide 143 is formed of opposing, fixed chute members 145 attached to thelower side of ROV 18. In another preferred embodiment, guide 143 isformed of opposing, movable traction members 147 attached to the lowerside of ROV 18. A non-limiting example of a traction member is a wheelor tractor track commonly utilized in a squirter engine to engage andpropel a non-rigid or semi-rigid line. In either case, line 144 isthreaded through guide 143 so as to be between the opposing members. Assuch, movement of ROV 18 in a forward direction, illustrated by arrows149, causes line 144, as well as OBS units 22 attached thereto, to bedrawn down underneath ROV 18 and to be passed through guide 143. As anOBS unit 22 passes through guide 143, it is caused to be coupled toseabed 140. In one embodiment, to enhance engagement of OBS units 22with seabed 140, guide 143 may include a plate 151 or similar structurepositioned between opposing members. As line 144 passed through guide143, an OBS unit 22 contacting plate 151 will be urged downward intocoupling contact with seabed 140.

In any event, preferably, opposing members are aligned so as to besubstantially parallel with the direction of forward movement of ROV 18.Forward movement of ROV 18 along a desired deployment line will therebycause line 144 to be drawn down and laid along the desired deploymentline. To the extent guide 143 utilizes traction members 147, suchmembers may be disposed to rotate counter to one another whilesimultaneously engaging line 144, thereby functioning to “squirt” line144 through guide 143 and providing a positive drive mechanism toactively pull line 144 down from the surface.

The apparatus and method in this embodiment provide an “on time” OBSunit delivery system so that OBS units 22 arrive for deployment just asROV 18 is moving into position on seabed 140. Such a system eliminatesthe need for the prior art basket system in which an ROV was constantlyrequired to return to a central distribution point, wasting valuabletime. Elimination of the prior art basket system also eliminatesindependent, free-floating lines in the water and the drawbacksassociated therewith. In contrast, line 144 of the invention is“controlled”, and hence the likelihood of entanglement with other linesis significantly reduced, since line 144 is paid out from the back deck142 at the water surface and secured by guided ROV 18 at the seabed 140.

Referring to FIG. 14, a retrieval system for line 144 is shown. Asillustrated, an anchor weight 160 may be attached to line 144 somedistance away from the last OBS unit 22 on line 144. Anchor 160 ispreferably positioned on the seabed 140 by ROV 18 so that the line 144is slack and not under tension between the last OBS unit 22 and anchor160. A positively buoyant buoy 162 is attached to anchor 160 by a buoyline 155. Buoy line 155 is of sufficient length to extend from anchor160 to the surface. In the preferred embodiment, to avoid interferencewith surface vessels, buoy 162 is releasably secured a desired distancebelow the surface by an acoustical release device 164 that attaches tobuoy line 155. Retrieval of OBS units 22 from seabed 140 is thusachieved by acoustically activating acoustical release 164, whereby buoy162 floats to the surface for recovery. Line 155, anchor 160 and line144 can then be “reeled in” so that OBS units 22 disposed on line 144are sequentially retrieved.

In each of the described embodiments of the invention, by utilizing anROV or similar remote deployment mechanism, OBS units can be placedaccurately on the seabed in the desired position. Likewise, properorientation can be ensured, as can a high degree of coupling. While thesystem has been described utilizing only one ROV, those skilled in theart will appreciate that such a system could easily utilize multiple ROVwithout creating the entanglement problems of the prior art since theROV, and hence the lines attached thereto, are all drivable. MultipleROVs also provide redundancy in the event that an ROV breaks down or isotherwise disabled. Thus, in the event of an ROV breakdown, operationscan continue while the disabled ROV is repaired. In this same vein,utilizing at least two ROVs, one ROV can always be shuttling between thesurface and the seabed while the other ROV is physically deploying unitson the seabed.

In the preferred embodiment, each OBS unit is wireless andself-contained so that no communication, control or operation action isrequired between the ROV and the OBS units. Preferably, operation of theOBS units has been initiated prior to deployment from the deck of thedeployment vessel, or alternatively, prior to handling by the ROV at theseabed. In this regard, each ROV 18 may be provided with a camera andeach OBS unit 22 may be provided with a visual beacon, such as a strobelight, which visual beacon is operative only when the OBS unit isoperating within predetermined parameters. To the extent a parameter isout of range or the unit is otherwise not functioning properly, thevisual beacon will indicate the malfunction. Once an OBS unit 22 hasbeen placed on the seabed, the camera on the ROV 18 can be utilized toensure desired operability of the OBS unit. As a non-limiting example,operability parameters may include, but are not limited to batterycharge, orientation, coupling, and recording parameters. Thus, in theevent an OBS unit parameter does not fall within the desired range, theproblem can be immediately identified while the ROV is “on site.” Hencecorrective measures can be taken or the defective ROV can be replacedwithout interfering with the subsequent seismic operations.

Alternatively, monitoring and control functions may be provided by awireless communication modem, such as, for example an acoustical orelectromagnetic device, disposed in OBS unit 22 and attached to ROV 18.In this case, an OBS unit may be checked concerning the aforementionedparameters and control commands may be given to the unit to do a varietyof things, such as, for example, starting and stopping recording,changing recording parameters, performing special tests, retrievingdata, etc. when the unit and ROV are within communication range.

The ROV/carrier system can also be utilized to retrieve deployed OBSunits from the seabed and transport them back to the surface vessel. Acarrier containing retrieved OBS units can be detached from the ROV atthe surface and moved to a location on the vessel for processing andservicing of the OBS units. Preferably, such units are removed from thecarrier and seismic data extraction takes place on the deck. Thereafter,the OBS units are charged, tested, re-synchronized, and OBS unitoperation is re-initiated. OBS units that have been processed in thisregard can be loaded back into the carrier for reuse.

Preferably, each OBS unit is activated while on-board the seismic vesseland deactivated once pulled from the ocean, such that it is continuouslyacquiring data from before the time the ROV begins a trip down to theseabed. However, as mentioned above, recording may be initiated remotelyusing wireless modems.

On the deck of the seismic vessel, carriers are preferably stackable inorder to maximize deck space. A robotic arm, overhead gantry, crane orthe like may be positioned on the deck to move carriers and ROVs.Likewise, the vessel would include an OBS unit handling system to loadand unload carriers, as well as to perform various tasks on the OBSunits, such as data extraction, testing and charging.

While certain features and embodiments of the invention have beendescribed in detail herein, it will be readily understood that theinvention encompasses all modifications and enhancements within thescope and spirit of the following claims.

1-127. (canceled)
 128. A method for deployment of ocean bottomseismometers (OBS) units on the ocean floor, said method comprising: a.providing a plurality of circular shaped, wireless, self-contained OBSunits, b. transporting said OBS units from a surface vessel to the oceanfloor; and c. utilizing an ROV to individually place the plurality ofcircular OBS units on the ocean floor, d. wherein said placement isaccomplished by engaging each circular shaped OBS unit coaxially with asuction cup and moving the OBS unit from a first location to the oceanfloor.
 129. The method of claim 128, wherein the step of transporting isaccomplished with a carrier loaded with a plurality of OBS units. 130.The method of claim 129, wherein the ROV transports the carrier to theocean floor.
 131. The method of claim 128, wherein the suction cup iscoaxially positioned utilizing a robotic arm secured to the ROV. 132.The method of claim 128, wherein the suction cup engages thesubstantially flat, top surface of the circular OBS units.
 133. Themethod of claim 128, further comprising the steps of a. providing acamera on said remotely operated vehicle; b. providing an indicator on aOBS and activating said indicator to indicate the operational status ofthe OBS; and c. utilizing said camera to view the indicator to ascertainthe operational status of the OBS.
 134. A system for deployment of oceanbottom seismometers (OBS), said system comprising: a. a plurality ofcircular shaped, wireless, self-contained OBS units, each having anupper surface; b. a carrier loaded with said circular shaped OBS units;c. a ROV; d. a robotic arm having a distal end and a proximal end, saidproximal end attached to the ROV; e. a suction mechanism attached to thedistal end of the robotic arm, said suction mechanism disposed to engagethe upper surface of an OBS.
 135. The system of claim 134, wherein saidcarrier is attached to said ROV.
 136. The system of claim 134, whereinsaid OBS unit comprises an external visual beacon and said ROV comprisesa camera.